Thesis (Ph.D.) - University of St Andrews, March 2008.

Thesis (Ph. D.)--University of California, San Diego, 1997. / Vita. Includes bibliographical references.

No description available.

Thesis (Ph. D.)--University of California, San Diego, 2001. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of California, San Diego, 2003. / Vita. Includes bibliographical references.

The purpose of this thesis is to analyze the viscoelastic properties of current large digital storage magnetic tape materials, using a custom ultra-low frequency dynamic mechanical analyzer (DMA). Through the correlated effects of frequency and temperature, the long term mechanical properties of the magnetic tape can be simulated and used for predictive analysis of long term storage quality and stability of each individual tape given applicable storage conditions. Two magnetic tapes of primary interest reviewed in this paper are both current leading high capacity tapes, one having a poly(ethylene naphthalate) or PEN substrate and the other an aromatic polyamide or ARAMID substrate. The phase angle between the two signals and the peak strain based elastic modulus (E) were then used to determine the storage modulus (E'), loss modulus (E"), and the loss tangent (tan 8). These viscoelastic characteristics of the material were determined for each individual experimental sample. The combined data was then used to create comparative plots of each sample type allowing for a more conclusive look at the magnetic tape properties under the given conditions. It is found that viscoelastic deformation, or energy loss in the material, increasingly occurs at low frequencies. These experiments also verify that viscoelastic loss also occurs due to molecular orientation and can have a large impact on results. A final comparison is also made between the two leading tape materials commonly used in industry currently by taking a direct look at relative loss in conjunction with the materials overall complex elastic modulus. This allows a more definitive strength comparison of the defined materials · under given conditions.

In the beginning of the twenty-first century, educational and commercial institutions have driven the demand for cheap and efficient data storage. The storage medium known as magnetic recording media has remained the mainstay for most computer systems due to its large storage capacity per dollar. With the recording media's ever-increasing storage density has come reductions in the magnetic grain size per bit. At the recording bit's density threshold, the magnetic grains become more susceptible to thermal activation, which can render the storage medium unusable. An accurate characterisation of the recording layer's sub-granular structure is essential for understanding the magnetic and thermal mechanisms of high-density recording media. Small-Angle Neutron Scattering (SANS) studies have been performed to investigate the magnetic and physical properties of longitudinal and perpendicular recording grains. The SANS studies of longitudinal magnetic recording media have probed the recording layer's magnetic grain size at a sub-nanometer resolution. In conjunction with these studies, SQUID magnetometry was used to characterise the recording grain's bulk magnetism. Measurements showed that the recording grain was composed of a ferromagnetic hard core (Co-enriched) and a weakly magnetic shell (Cr-enriched). These results provided important information on the grain's magnetic anisotropy, which determines the recording media's magnetic stability. The polarised SANS studies were used to characterise the recording layer's physical granular structure. It was shown that the physical grain size was comparable to its magnetic counterpart. These physical measurements provided insight into the recording grain's chemical composition. The magnetic properties of perpendicular magnetic recording media were studied using SANS and VSM measurements. The neutron scattering studies revealed that the recording grain was composed of a hard ferromagnetic centre enriched with cobalt. The VSM studies showed that the magnetic recording grains exhibited a large perpendicular magnetic anisotropy. These combined studies provided information on the recording grain's ferromagnetic composition and magnetic stability. The polarised SANS measurements showed the physical grain size to be slightly smaller than its magnetic counterpart. This size difference was attributed to the non-magnetic grain boundary composed of SiO2. The boundary thickness determined the degree of inter-granular exchange coupling. Further polarised studies investigated the recording layers switching behaviour, which revealed more information on the grain's magnetic stability.